ooooooo your first demo!! I love them!
I find actually that the over 50's usually like something a wee bit different. You'll find that most of them think they know about flowers etc, so using something different from the usual cars and xanths has proven very successful. Also, impress them by using variety names etc...
As to what to talk about, I don't usually even talk about the flowers, well not much anyway. Tell them about your shop, what you can do, yadda yadda. They'll pay much more attention